Urea-formaldehyde composition



" Patented Mar. 7, 1944 UNITED STATES PATENT OFFICE mesne assignments, to

Libbey-Owens-Ford Glass Company, a corporation of Ohio No Drawing. Application March 27, 1943, Serial No. 480,849

4 Claims.

The invention relates to a thermosetting composition comprising a urea-formaldehyde reaction product and a novel latent curing catalyst.

When a thermosetting composition is shaped in a mold under pressure at an elevated temperature, it first softens and then hardens at the molding temperature, whereas a thermoplastic .composition that is hot-molded remains soft until the molded piece is cooled. Thus an article can be molded from a thermosetting composition by simply placing the composition in a hot mold, closing the mold, and then removing the finished article after a relatively short time while the mold is still hot. The molding of an article from a thermoplastic composition presents a more complex problem, because an article molded from such a composition must be cooled before the mold is opened to prevent blisteringv and other urea-formaldehyde .composition cannot be supplied in an acid condition by a manufacturer, because a urea-formaldehyde composition that is acid is unstable in storage. If it is acid, a urea-formaldehyde composition gradually becomes infusible at ordinary temperatures. Such a composition could not be sold by a manufacdeformation which would occur if the mold were I opened while the thermoplastic material was still hot.

The length of time for which a molding composition must be left in the mold is one of the factors determining the cost of articles molded from the composition. A composition that must be left in the mold twice as long as another composition requires about twice as much molding equipment for the samevolume of production, and hot-molding equipment is expensive.

A urea-formaldehyde reaction product is thermosetting in the presence of an acid substance in that it is cured" or transformed by heat from a fusible composition into an infusible resin. In order to cause such transformation to take place, an acid substance must be present to act as a catalyst. In the molding of an article from a urea-formaldehyde composition, it is necessary to leave the composition in the hot mold for a short time after the mom has been closed in order to complete the transformation to the iniusible resin so as to produce an article of optimum quality. The length of time for which it is necessary to leave a urea-formaldehyde composition in the mold varies with the degree of acidity produced by the acid substance used as a catalyst: the more acid the composition, the. shorter the time required to complete the transformation to an infusible resin in the hot mold. There is, of course, a'demand for urea-formaldehyde molding compositions that are completely converted into an infusible resin so that the finished article can be removed from the mold a relatively short time after the mold has been closed.

In spite of the advantage of acidity during the molding of a urea-formaldehyde composition. a

turerbecause it would be infusible and worthless by the time it reached the hands of a molder.

Even slight acidity which causes the composition to become infusible very gradually would make the composition commercially unacceptable, because the plasticity and other molding properties of such a composition would be wholly dependent upon the atmospheric temperature prevailing and the number of hours elapsed between the production of the finished composition by the manufacturer and the molding of the composition by the user. A user who molds articles from a urea-formaldehyde composition must select a composition of the proper plasticity and test the composition by molding it under various conditions to determine the exact conditions required to give the desired results. In order to maintain the quality of the product, he must then continue to use a composition of exactly the same plasticity and to mold it under exactly the same conditions. If the composition used by the molder is unstable and has molding properties which vary with the length of time elapsed since the composition was produced, it is impossible for the molder to mold successive articles from the composition with satisfactory results.

A latent curing catalyst in a urea-formaldehyde composition is an ingredient that causes the transformation of the composition to an infusible resin in a hot mold, but does not materially impair the stability of the composition in storage 'at ordinary temperatures prior to hot'molding.

True latent curing catalysts are very rare. A latent curing catalyst may be alkaline, neutral or so slightly acid that it does not appreciably acidiiy a urea-formaldehyde composition when added thereto. It is believed that such a substance breaks up or undergoes molecular rearformaldehyde reaction product into an iniusible resin.

A urea-formaldehyde molding composition contains an appreciable amount of moisture and frequently is kept in storage. for weeks at a time before being used. Many substances that might be expected to decompose to form acids under molding conditions suffer the same decomposition within a few hours after being intimately mixed with a urea-formaldehyde composition, and therefore are not latent curing catalysts. Moreover, the behavior of a substance when present as a minor ingredient in a molding composition andsubjected to molding pressure! at the molding temperature of 270 F. to 330 F. cannot be predicted from its behavior when subjected by itself to such a temperature under atmospheric pressure. Most of the potentially acid substances that do not impair the stability of a molding composition when incorporated therewith fail to cause the transformation of the composition to an infusible resin in a hot mold.

The principal object of the invention is to provide a thermosetting urea-formaldehyde composition containing a novel latent curing catalyst. More specific objects and advantages are apparent from the description, which discloses and illustrates the invention, and is not intended to impose limitations upon the claims.

A thermosetting composition embodying the invention comprises a urea-formaldehyde reaction product and a latent curing catalyst selected from the class consisting of phenyl diame ido phosphate, cresyl diamido phosphates and xylenyl. diamido phosphates. The preferred latent curing catalyst is phenyl diamido phos phate, having the structural formula but mor p-cresyl diamido phosphate, having the structural formula v NH:

or a x'ylenyl diamido phosphate, having the struc-' tural formula cm /NHa AG on, \NHZ may be employed as the latent curing catalyst if desired. The benzene ring is enclosed in parentheses in each of the latter two structural formulae to indicate that any of the three position isomers of cresyl diamido phosphate or any of the six position isomers of xylenyl diamido phosphate may be used.

In the preparation of a reaction product of urea and formaldehyde for use in a composition embodying the invention, the urea may be re-- acted either with formaldehyde or with a polymer thereof, such as paraformaldehyde. Although under some conditions it is permissible to react dry urea with dry paraformaldehyde, the

reaction is preferably carried out in an aqueous cess of formaldehyde above such'maximum or a smaller proportion ranging down to about one mol of formaldehyde for each mol of urea may be used for the reaction if desired. Because of the complexity of the molecules of the reaction products that are produced, the proportion of formaldehyde actually reacting with the urea may vary freely between the limits stated. The reaction proceeds at ordinary temperatures, but heat may be used to shorten the time of reaction if desired. A reaction product may be prepared 'by carrying the reaction of the urea and formaldehyde only to its earliest stage, for example the stage at which the urea and formaldehyde havejust been brought into solution together, or the reaction may be carried to any further stage at which the reaction product is still fusible.

The preferred method of preparing a molding composition consists in preparing an aqueous solution of a urea-formaldeyhde reaction product, then impregnating cellulosic material with the solution and drying. Although alpha cellulose is the purest and lightest-colored cellulosic material that may be employed, any other cellulosic material, such as wood flour, wood pulp, newsprint, printed newspaper, sawdust, shavings, walnut shell flour, or ground corn cobs may be used. The impregnated and dried cellulosic material is preferably ground to a fine powder in order to produce a homogeneous composition, and the latent curing catalystis preferably incorporated during the grinding stage.

The customary modifiers such as hot-plate lubricants, opacifiers, pigments and other coloring matter may also be incorporated during the grinding. The fine powder so obtained may be formed into coarse granules, or into solid blanks or preforms of the proper sizes for use in various molds. Molded articles may'beproduced in the usual manner by compressing the composition in a closed mold under a pressure of one to four tons per square inch of projected area and at a temperature of 270-330 F. The proportion of cellulosic material in a dry composition enrbodying the invention is preferably from about 30 to about 40 per cent, but may range from 0 7 per cent to as much as 60 per cent in the case of a dense cellulosic material, such as'walnut shell flour.

which causes the hardening to take place at the desired speed, butthe usual proportion is from about one-half to about one per cent of the weight of "the molding composition.

Example After alpha cellulose fiber ,parts by weight) has been impregnated with an aqueous solution containing parts of a urea-form aldehyde reaction product, the impregnated material is dried by any of the usual drying meth ods. Heat may be used as is customary to ex-' pedite the drying, and drying by means ofa stream of air is convenient. The dried material I is ground in a ball mill together with about one per cent of its weight of phenyl diamido phos phate and any other desired modifiers. The resulting powder-is usable as a molding composition for many applications but can be granulated I The proportion of the latent curing catalyst employed is simply that proportion urea-formaldehyde reaction product and a latent curing catalyst selected from the class conslsting of phenyl diamido phosphate, cresyl diamido phosphates and xylenyl diamido phosphates.

2. A thermosetting composition comprising a urea-formaldehyde reaction product, cellulosic material and a latent curing catalyst selected from the class consisting of phenyl diamido phosphate,

cresyl diamido phosphates and 10 xylenyl diamido phosphates.

3. A thermosetting composition comprising a urea-formaldehyde reaction product and phenyl diamido phosphate as a latent curing catalyst.

4. A thermosetting composition comprising a urea-formaldehyde reaction product and an amount of phenyl diamido phosphate equal to about one per cent, of the weight of the composition, as a latent curing catalyst.

JOHN KENSON SIMONS. 

